A DC motor is used to drive an attached mechanical device, which is typically coupled to the motor through an intermediary gearing system such as a gearbox. If the attached device is suddenly stopped, it can produce mechanical shock that is transmitted into the driving motor and gearbox. The mechanical shock can occur when the part of the device that is in motion hits an end stop or other obstruction in the travel path.
If the mechanical shock is sufficiently strong or occurs repeatedly, the motor and gearbox can be damaged and cause the system to fail to operate. The mechanical shock can damage the motor by twisting the motor shaft or loosening or breaking the motor's mounting to the device. The mechanical shock can damage the gearbox by cracking the gears, breaking off gear teeth, or loosening or breaking the gearbox's mounting to the device.
A common solution to protect a device from this kind of mechanical shock is to pad the travel end stops with a shock absorbing material, such as rubber. This solution requires extra cost and does not protect against an unanticipated obstruction being placed maliciously or unintentionally in the travel path.
Another common solution is to strengthen the motor and gearbox materials to handle the potential shock. This solution usually adds significant cost to the manufacture of the system.
Yet another common solution is to slow the motion of the device down to the point where a sudden stop will not produce enough mechanical shock to damage the system. This solution can adversely effect the operation of the system.